This invention relates to a tire pressure indicator and, in particular, to a tire pressure indicator for providing an easily viewed, qualitative indication of the air pressure within a pneumatic tire.
The motoring public is generally aware of the need to have tires properly inflated for optimum tire life and performance. Under-inflated tires wear more quickly and degrade the handling characteristics of a car. The problem is that the tedium of measuring the pressure in each tire causes many motorists to forego measuring the pressure in the tires and rely on a visual inspection instead. A visual inspection is inadequate, particularly when a car is equipped with radial tires, because a sidewall bulge is present even in properly inflated tires.
In the prior art, a number of qualitative indicators have been proposed for inclusion in the valve cap on each wheel. In general, these devices are relatively expensive to manufacture and difficult to read. One source of the difficulty is that the valve stem points from the rim of the wheel in such a way that the motorist is generally looking at the end of the cap, which typically has a diameter of one quarter of an inch or less. Another source of the difficulty is that the wheel can come to rest with the valve stem at any position, e.g. top center, bottom center, or anywhere in between. The result is that the indicator is often at an awkward angle for reading and must be read from a short distance, e.g. a couple of feet.
U.S. Pat. No. 4,606,931--Achterholt--discloses a valve cap with a pressure drop indicator in which a diaphragm moves a sliding indicator inward through the valve cap. A blade like marking member within the indicator remains extended when the indicator moves inward to show that the pressure has dropped within the tire. The blade is contained within a transparent end cap and must be positioned correctly for someone to see either side of the blade rather than an edge.
U.S. Pat. Nos. 4,601,254--Huang et al.--and 3,164,125--Stuart--disclose valve caps with frangible end portions for indicating low pressure. Once the end portions break, the indicator must be replaced and the motorist is without an indicator until the spent valve cap is replaced.
U.S. Pat. Nos. 2,704,045--Riesing, 3,208,425--Jousma et al., 3,380,427--Rubin, and 3,780,693--Parr each disclose a pressure indicator in which a marker is viewed through a small port in the indicator. As with the indicator of Achterholt, the viewing angle is often awkward because of the rotational position of the indicator on the wheel. The Rubin patent discloses a gauge which is at a right angle to the longitudinal axis of the valve stem. Nevertheless, the tire must be rotated to the correct position in order to see the indicia on the gauge.
In view of the foregoing, it is therefore an object of the invention to provide a qualitative pressure indicator for a pneumatic tire in which the indicator can be read irrespective of the rotational position of the tire.
Another object of the invention is to provide a pressure indicator for a pneumatic tire in which a qualitative display can be seen from all angles through a transparent cap.